The present invention relates to an improved process for extracting uranium from ores by pressure leaching or lixivation. More particularly, the invention is directed to pressure leaching under high temperature and pressure conditions and oxidation with gaseous oxygen in order to extract a uranium product at high yields and of a high degree of purity. The invention has particular importance in continuous extraction processes utilizing a tube reactor.
The basic concept of acid or alkaline leaching of uranium from ores is well understood. However, in conventional leaching processes, relatively high amounts of impurities are also dissolved in the leaching solution. Furthermore, in ores such as gold sands, slate, arenaceous quartzes, and silicates, the uranium content is usually below 1% on down to less than 0.1% in low grade ores. A central problem has thus been to devise an economically feasible extraction system capable of processing large amounts of ore continuously with as low as possible a retention time in the system while extracting as high as possible a yield from the ore and with a minimum of impurities.
Extensive work has been done with pressure leaching of uranium-bearing ore in laboratory batch testing. Pilot projects for the continuous processing of ore by pressure leaching have also been undertaken. For example, in one system that has been studied, an ore slurry is cascaded in a series of autoclaves, and steam, oxygen, and sulphuric acid are injected to dissolve the uranium into soluble, hexavalent uranium oxide form which can then be separated from the solids in suspension and refined. However, this type of autoclave system typically requires retention of the slurry for long periods of time of the order of about 60 to 120 minutes in order to achieve the higher yields of 85 to 95% dissolved uranium oxide in the leaching solution.
It is an object of the present invention to provide a method of rapidly and continuously extracting high yields of uranium from ores with a minimum of impurities.
It is another object of the invention to devise a method of extracting high yields of relatively pure uranium through the pressure leaching of ores in a tube reactor system, and to provide such a system which utilizes excess heat in the system and minimizes its impact on the environment.
It is a further object of the invention to specify the optimal parameters and critical operating conditions for a tube reactor system for the continuous, high-yield extraction of a high-purity uranium product from ores.